1. Field of the Invention
The present invention relates to a metal bonded drilling tool and a metal bonded chamfering tool.
2. Description of the Related Art
In the case of drilling a hole in a stone, concrete, or hard wall, it is conventionally general to mount a diamond core bit on an electric drill. According to this drilling method, however, it is not possible to instantaneously form a cut on a stone or the like, because the rotational speed of the diamond core bit is as low as 1000 to 2700 rpm. To cope with this problem, a center stick is attached to the diamond core bit at a central portion thereof. After forming a small cut on a subject material by means of the diamond core bit on the basis of the center stick, the center stick is removed and a hole is next drilled by only the core bit.
The diamond core bit is an impregnated sintered tool wherein the amount of projection of diamond abrasive grains is small. Accordingly, unless this tool is operated in a wet condition (where water is supplied during drilling), a drilling performance cannot be exhibited. Actually, water is supplied from a hose during drilling, or a sponge containing water is preliminarily inserted in the diamond core bit and the water is supplied from the sponge during drilling.
There is another method without mounting the center stick at the central portion of the diamond core bit. In this method, a guide ring is mounted on a subject material with an adhesive sheet interposed therebetween, and a hole is drilled on the basis of the guide ring by the diamond core bit mounted on the electric drill. According to this method, however, a drilling operation is troublesome and it cannot be performed at a site where no stains are allowed, such as the interior, because a wet condition is adopted.
As still another method, a boring machine for stones is fixed by screws to the surface of a subject material, and an impregnated type core drill is used to drill a hole in the subject material. However, since the boring machine is fixed by screws to the surface of the subject material before drilling, threaded holes for the screws must be preliminarily formed in the subject material and the work for mounting the boring machine is troublesome. Furthermore, also in this method, drilling must be performed in a wet condition.
On the other hand, in chamfering a hole formed on a stone or the like, a grinding wheel having a small diameter is mounted on a disc grinder, and the outer circumferential edge of the grinding wheel is used to chamfer the hole. As another method, a cup wheel having a small diameter is mounted on a disc grinder, and the outer circumferential edge of the cup wheel at a front end portion thereof is used to chamfer a hole formed on a stone or the like. According to these chamfering methods, however, the life of the grinding wheel or the cup wheel becomes short and there are variations in appearance of the chamfered hole obtained by the grinding wheel or the cup wheel, because the outer circumferential edge of the grinding wheel or the cup wheel is used for chamfering. Further, it is impossible to perform chamfering of a hole having a diameter smaller than the diameter of the grinding wheel or the cup wheel.
It is therefore an object of the present invention to provide a metal bonded drilling tool which can easily drill a hole in a hard material such as a stone or concrete without the use of a positioning jig for drilling.
It is another object of the present invention to provide a metal bonded chamfering tool which can chamfer a small hole formed in a hard material such as a stone or concrete.
In accordance with an aspect of the present invention, there is provided a metal bonded drilling tool comprising a cylindrical body having an open front end portion; a shank integral with said cylindrical body and having a threaded hole for use in mounting said tool to a rotary tool operating at a rotational speed of 5000 rpm or more; and numerous abrasive grains brazed to a front edge of said cylindrical body and to inner and outer cylindrical surfaces of said front end portion of said cylindrical body by a brazing member.
In accordance with another aspect of the present invention, there is provided a metal bonded chamfering tool comprising a cylindrical body having an open front end portion; a shank integral with said cylindrical body and having a threaded hole for use in mounting said tool to a rotary tool operating at a rotational speed of 5000 rpm or more; and numerous abrasive grains brazed to an outer cylindrical surface of said cylindrical body by a brazing member.
Preferably, said brazing member comprises a bond member formed primarily of copper alloy, said bond member containing a material selected from the group consisting of Ti, Al, and a mixture thereof; an average abrasive grain projection height is set to 30% or more of an average abrasive grain diameter, where said abrasive grain projection height is defined as the distance between the surface of a deepest portion of said bond member present between any two adjacent ones of said abrasive grains and the top of each of said two adjacent abrasive grains; and an average abrasive grain spacing is set to 200% or more of said average abrasive grain diameter, where said abrasive grain spacing is defined as the distance between the tops of said two adjacent abrasive grains.
Preferably, said copper alloy is selected from the group consisting of bronze containing 10 to 33 wt. % of Sn, brass containing 5 to 20 wt. % of Zn, and aluminum bronze containing 5 to 20 wt. % of Al. More preferably, said abrasive grains are selected from the group consisting of diamond, cubic boron nitride, silicon carbide, and cemented carbide powder.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.